I purchased a phantom 4 pro v2 from a friend.  I cannot read the serial number in the battery tray so i can register it properly on the FAA drone zone site. Also the software will start to download and then ask if I want to continue.  After a few times it fails and i have to start over.  I got no manuals with it.

Hi, Bad05ford. Thanks for reaching out, and apologies for the inconvenience. For the firmware update failure issue, kindly refer to the following recommendations:
1. Before updating, ensure that the battery level of the device (remote controller or aircraft) is above 50%.
2. While updating, do not power off the aircraft or disconnect the USB cable. Otherwise, the update may fail.
3. While updating, the device may automatically reboot several times. When rebooting, it is normal for the remote controller to disconnect from the aircraft automatically. Do nothing before the update is completed to avoid affecting the normal updating process.
To update, please perform as follows:
1. Power off and reboot the remote controller and aircraft. Try updating again.
2. Ensure you use the correct DJI Assistant 2 version. You may uninstall the one you have and reinstall it from this link and try again.
If the issue remains, please post a screenshot of the error message here. Regarding the battery SN, we'll forward them to our team for feedback. Thanks for your cooperation.

Managed to update aircraft with usb cable. remote wouldnt pull up firmware on laptop but it updated after the aircraft was updated. Flew good yesterday, have another issue/question but made another post. Thanks for reply.